National Institute for Occupational Safety and Health

“ Data can be recorded directly off the screen in μm and later converted to μm by computer. NOTE 2: For fibers which extend beyond the field of view, the fiber must be moved and superimposed upon the scale until its entire length has been measured. (b) When a fiber has been sized, return to the lower magnification and continue the traverse of the grid area to the next fiber. d. Record the following fiber counts: (1) fs, f b = number of asbestos fibers in the grid openings analyzed on the sample filter and corresponding field blank, respectively. ”

“ The level of acetone should be just high enough to saturate the filter paper without creating puddles. Remove about a quarter section of the carbon-coated filter from the glass slide using a surgical knife and tweezers. Carefully place the excised filter, carbon side down, on the appropriately-labeled grid in the acetone-saturated petri dish. When all filter sections have been transferred, slowly add more solvent to the wedge-shaped trough to raise the acetone level as high as possible without disturbing the sample preparations. ”

“ Count only grid openings that have the carbon film intact. At 500 to 1000X magnification, begin counting at one end of the grid and systematically traverse the grid by rows, reversing direction at row ends. Select the number of fields per traverse based on the loading indicated in the initial scan. Count at least 2 field blanks per sample set to document possible contamination of the samples. Count fibers using the following rules: (1) Count all particles with diameter greater than 0.25 μm that meet the definition of a fiber (aspect ratio ≥3:1, longer than 5 μm) . ”

“ Other amphibole particles that have aspect ratios greater than 3:1 and elemental compositions similar to the asbestos minerals may interfere in the TEM analysis. Some non-amphibole minerals may give electron diffraction patterns similar to amphiboles. High concentrations of background dust interfere with fiber identification. Some non-asbestos amphibole m inerals may give electron diffraction patterns similar to asbestos amphiboles. ”

“ Estimate the elemental peak heights visually as follows: (1) Normalize all peaks to silicon (assigned an arbitrary value of 10) . (2) Visually interpret all other peaks present and assign values relative to the silicon peak. ”

“ There are, however, several minerals (e.g., pyroxenes, massive amphiboles, and talc fibers) which are chemically similar to asbestos and can be considered interferences. The presence of these substances may warrant the use of more powerful diffraction pattern analysis before positive identification can be made. If interferences are suspected, morphology can play an important role in making positive identification. Obtain EDX spectra in either the TEM or STEM modes from fibers on field samples using the procedure of step 18. Using the diffraction pattern and EDX spectrum, classify the fiber: a. ”

“ Acetone. (See SPECIAL PRECAUTIONS.)
EQUIPMENT: 1. Sampler: field monitor, 25-mm, three-piece cassette with ca. 50-mm electrically-conductive extension cowl, cellulose ester membrane filter, 0.45- to 1.2-μm pore size, and backup pad. NOTE 1: Analyze representative filters for fiber background before use. Discard the filter lot if mean count is >5 fibers/100 fields. These are defined as laboratory blanks. NOTE 2: Use an electrically-conductive extension cowl to reduce electrostatic effects on fiber sampling and during sample shipment. Ground the cowl when possible during sampling. ”